New Thinking On Lighting Design
April 01, 2003
Appeared in Building Operating Management/FacilitiesNet
In an era of cost cutting, the energy used for lighting systems in todays facilities is often an apt target for energy efficiency upgrades. And for good reason: lighting systems typically account for up to 30 percent of a facilitys energy use. Energy-efficient lighting designs can often slash lighting energy use by up to 50 percent.
In existing buildings, depending on the condition of the fixtures, this can be easily accomplished with a one-for-one replacement: T12s for T8s; magnetic ballasts for electronic ones. While this approach might be a safe way to reduce energy use, its not a sure way of improving the lighting in a space or reducing energy use as much as it could be. Yet this approach is often used.
That same tactic is often employed in the design of new buildings. Despite the advances made in lighting hardware and system design, older lighting designs from one building are often transferred into a new building with only passing regard for a new buildings site, floorplate configuration or use. True, the design may be tweaked; the number of recessed 2-by-4-foot fixtures still among the most commonly specified fixtures for speculative office buildings may vary, but usually an existing strategy is reused.
Experts say this strategy is often employed as a least-cost alternative to spending extra money on lighting designs and more expensive fixtures. But the reality is that it is often not the most energy efficient or effective and may not be the least-expensive strategy. Existing problems with the old design, such as too much light, too little light, discomfort, glare and unattractive appearance, are just transplanted to the new building. Even too little light, if poorly positioned, can be wasted energy. In addition, any one of these problems also could affect productivity and even leasing, as todays tenants look for attractive, comfortable spaces to rent.
Because the lighting system has the power to affect a new buildings bottom line in multiple ways, it is critical to design the lighting system for each new building carefully, addressing specific elements of the building space and occupant needs.
Two trends in the last 10 years have changed the way most experts look at lighting design. The first is the dramatic improvement and cost-effectiveness of the technology. Todays lamps provide more lumens per watt than older ones, and the fixtures have been redesigned to more effectively use this light. But perhaps an even more important trend has been the development in understanding how lighting affects a buildings space, says Maryann Hay, director of lighting design for Syska Hennesey Group. Computers, for example, are not only used more during the day, they are used by nearly everyone. This presents numerous problems for older lighting designs, such as 2-by-4 recessed fixtures, that can cause glare on computer screens.
The 2-by-4 fixture with an 18-cell parabolic louver may have served a purpose years ago, but it shouldnt be the direction we are going today, Hay says. Corporate owners are leading the trend, she says, but the speculative market is still lagging.
These fixtures have gained a low-cost reputation, largely because they often are spread out into a less-dense matrix than a prudent design might allow. This lighting tactic is possible because, even sparingly spaced, these fixtures usually provide more than enough light. The design is ineffective, however, because the light might not fall where its needed. This can have a big effect on employees and their work methods, especially when space configurations are constantly changing. This also could have an impact on the speculative office market.
The watchword in any speculative or corporate project these days is flexibility, says Gary Steffy, president of Gary Steffy Lighting Design. The lighting system has to respond to turnover and high churn rates to be cost-effective.
Developers and tenants typically want 50 footcandles on the work surface. But when tenants move in, partitions go up. This blocks some of the light from recessed fixtures. Because there is no overlap of light, there are dark areas on work surfaces and walls. Either tenants overcompensate for the bad design with more task lighting or owners install more recessed fixtures. This can lead to more watts per square foot than a facility was originally designed for.
What an owner or an occupant really wants is a relatively low or moderate level of ambient light about 25 to 35 footcandles, Steffy says. If its done using direct-indirect or indirect fixtures, then it doesnt matter where someone sets up partitions. An occupant or a tenant can add task lighting to bring the light levels up to about 50 to 60 footcandles at the work surface.
To provide this kind of coverage using recessed fixtures would require a greater density of fixtures. That would push the cost of this low-cost alternative closer to that of a well-designed system using indirect lighting and pendant fixtures, Steffy says.
To avoid problems with glare and dark areas on the underside of the fixture, an indirect-direct lighting fixture should provide 2 to 6 percent direct lighting component, says David Nelson, a principal with Clanton and Associates. More direct light than that is acceptable if energy efficiency is paramount, Steffy says. In that case, up to 30 percent direct lighting may be used. But, he says, if the space is open office space where computers are used, that much direct lighting is going to cause a glare problem.
To provide the right balance of light, more and more owners are using direct-indirect pendant fixtures. These fixtures cost more than 2-by-4 recessed fixtures perhaps one and half times as much but when installation costs are included, the cost difference might disappear.
Nelson says that when considering all the costs involved technology and installation there is no cost difference between a good direct-lighting system using 2-by-4s and an indirect lighting system using 2-by-4s. And there is probably only a 5 percent cost premium with an indirect-direct system using pendants when installation of these fixtures is considered.
Recessed fixtures cost between $60 and $80, plus all the junction boxes and wiring that is needed, and the labor to install it. Nelson says an 8-foot pendant is much easier to install, taking less labor, and has one junction box for an entire row of fixtures, saving on material and equipment. You can make up the difference between the two with labor and some material savings, he says.
Finding the most effective way to use light is the first place to start to realize a cost-effective system.
Efficiency means finding ways to direct light only where it is needed, Steffy says. It doesnt mean necessarily less light; it doesnt mean blasting even energy-efficient light; it means using only as much as you need where you need it.
Layers of light
Lighting experts perceive lighting designs in two or three layers with an energy-use target, driven by ASHRAE/IESNA Standard 90.1-2001 and local energy codes, of 1.3 to 1.9 watts per square foot depending on the type of office and the tasks involved.
However, with properly selected luminaires and lamp wattages, along with electronic ballasts and carefully planned layouts, a typical open office lighting scheme might connect at 1.25 watts per square foot.
The first step is to consider a low to moderate level of ambient light, typically provided by recessed or pendant fixtures. The energy use should be about 0.75 watts per square foot.
A second layer is task lighting, integrated into furniture or free-standing, at about 0.3 watts per square foot.
A third, optional layer is accent lighting. The lighting typically focuses on specific architectural features or artwork. Accent lighting typically uses only about 0.2 watts per square foot.
The key to making all this work cost effectively is an integrated design. When an owner is thinking about the glazing, HVAC system or ceiling height, he or she should also be thinking about lighting design. And with todays sophisticated modeling programs, the impact of lighting design on a space and an owners bottom line can be fairly easily determined.
Ive seen even the most experienced designers surprised by the results of the output of a computer model, Nelson says. In addition to helping fine-tune the design and providing the most light for the buck, modeling can help reduce change orders. With integrated design, you rarely have systems that dont fit the space.
While the lighting budget may be 5 to 10 percent of a total project budget, lightings impact on the project can be huge, Hay says. And owners, especially corporate owners, are realizing lightings importance on staff needs and productivity.
Lighting technology and design have responded to needs to improve productivity and meet cost-cutting agendas during the last few years
For pendants or recessed fixtures, T8s are a standard spec for new buildings now, but increasingly T5s are being used. I see about 5 percent of the designs using T5s, but in five years I think they might be the base system for new construction, Steffy says.
T5s have several advantages over T8s. T5s offer more lumens per watt so they are less expensive to operate. This intensity of light, however, has to be treated more carefully than T8s. Even if they werent metric sizes, T5s couldnt and shouldnt be a simple replacement for T8s, Steffy says.
Standard T5s and T8s have about the same lamp life: 20,000 hours. But T5s use 40 percent less glass, 40 percent less phosphorous and less mercury.
Some T8s offer longer lamp lives up to 30,000 hours but are more expensive, require special ballasts and might have very specific on-off requirements that could make them inappropriate for use with lighting sensors.
Controls are another technology that might look expensive at first but can save a significant amount of energy dollars while providing a more comfortable workplace for the occupant.
Control technology has come a long way, Nelson says, and if owners are reporting any problems, the problems almost always have to do with the design or installation and not the technology. To prevent problems, however, controls have to be a forethought in the design of the building and installed carefully.
Most control manufacturers today will help with the design at no extra cost and even commission the controls at no or at a very low cost, Nelson says.
Occupancy sensors for conference rooms and private offices are becoming a standard design option nationally, Hay says. Large office areas are generally on time-clock type devices. But on the West Coast, especially in California where control use is being driven by energy-use legislation, lighting controls are being integrated with the energy management system.
Zone controls are getting more popular, Steffy says, and the zones are getting smaller, improving the controls cost, flexibility and effectiveness. Zone controls allow facility executives to control lighting in different parts of the building from a central location. New digital control language is making this easier. Because zone control is an added expense to the system, it is more prevalent where codes or utility costs are driving its use.
No matter the cost of lighting design and technology, some building owners are not going to bother with new ideas, and what worked in the past will be used in the future. But this perspective is changing as owners and tenants look at the cost of operating a business and realize the impact of lighting on the bottom line.
If someone is looking at the cheapest system and concerned only about the bottom line, a well-designed indirect lighting scheme isnt going to pan out, Steffy says. But if flexibility, quality and energy efficiency are of any concern, then a well-designed system should be part of the plan. And the fact is, some of this might be out of the owners hands in the years to come. It will be tenant-driven.